North American Veterinary Licensing Examination (NAVLE) Practice Test

What is the most likely diagnosis for a 5-year-old male castrated Mastiff presenting with left pelvic limb lameness and a clicking sound in the stifle during manipulation?

1. Left luxating patella

2. Left cranial cruciate ligament rupture with meniscal cartilage tear

3. Left cranial cruciate ligament rupture with no meniscal cartilage tear

4. Left caudal cruciate ligament rupture with no meniscal cartilage tear

The correct answer is: Left cranial cruciate ligament rupture with meniscal cartilage tear

The most likely diagnosis for the presented case, which involves a 5-year-old male castrated Mastiff with left pelvic limb lameness and a clicking sound in the stifle during manipulation, is left cranial cruciate ligament rupture with meniscal cartilage tear. In dogs, cranial cruciate ligament (CCL) injuries are common, especially in larger breeds like Mastiffs. The clinical signs of lameness and joint instability can manifest due to the ligament's role in stabilizing the knee joint. The clicking sound during manipulation of the stifle indicates that the joint may be affected by incomplete joint congruity, possibly associated with meniscal injury, which frequently occurs alongside CCL tears. A meniscal tear often presents as a 'clicking' or 'catching' sensation when the joint is moved due to the damaged cartilage shifting within the stifle. This clicking, combined with the lameness demonstrated by the dog, strongly suggests a concurrent meniscal tear, which is a common complication when there is a CCL rupture. Other conditions could lead to similar symptoms, but the specific combination of lameness and the clicking sound in an older dog like this Mastiff points toward the more complex diagnosis of a CCL